Development of a coherent Doppler lidar for precision

Development of a coherent Doppler lidar for precision maneuvering and landing of space vehicles Farzin Amzajerdian, Glenn D. Hines, Diego F. Pierrottet, Bruce W. Barnes, Aram Gragossian, Mitchell J. Davis, Tak-kwong Ng, Alexander D. Scammell, Adam Ben Shabat, Larry B. Petway, and John M. Carson NASA Langley Research Center 19 th Coherent Laser Radar Conference June 18 -21, 2018

Frequency Modulated, Continuous Wave (FMCW) Waveform 3 segments waveform minimizes false alarms due to zero-crossing and signal ambiguity 2

Navigation Doppler Lidar (NDL) Ø NDL Measures velocity and range along three different laser beams Ø Simultaneous line-of-sight measurements are used to estimate: § Velocity Vector (V) § Altitude relative to local ground (No IMU data required) 3

NDL Replaces Radars on Space Vehicles Ø Past landing missions used radars for vehicle position and velocity data in absence of GPS Ø NDL offers an order of magnitude higher precision and much higher data quality (low false alarms) while reducing required size, mass, and power Ø NDL enables “precision navigation” to the designated landing location Ø NDL enables “well-controlled” descent, landing, and ascent maneuvers to within a few cm/sec • Reduced touchdown impact loads lower lander mass • Optimized fuel consumption lower mass and risk 4

NDL development from breadboard to fully-autonomous prototype rocket-powered free-flyer vehicles 2008 Brea dboa rd w ithou 2010 proc ~200 kg essi t real-tim ng e GEN 1: ~ 60 kg 2012 Fully GEN 2: 28 kg -Aut 2014 onom ous GEN 2. 1: 17 kg Prot otyp e 2017 GEN 3: 10 kg 5

GEN 3 NDL § Fully-autonomous operation § Integrated real-time processors § Robust operation onboard different terrestrial vehicles Chassis 11”x 9”x 8” Optical Head 2” lenses 6

NDL Characterization Operational Range Measurements at Langley AFB Runway Gantry Tests NDL Setup NDL Optical Head Calibrated Target on back of a truck driven on the runway 7

NDL Operational Range Measurement Mean Intensity

Maximum Operational Range Predications Relative Signal Intensity Ø Maximum operational ranges in Mars and Moon extrapolated from measured data • Mars 5. 7 km • Moon 7. 5 km Lidar Equation Target reflectivity = 0. 5 Humidity = 70% Visibility = 17 km Moderate Turbulence Cn 2 = 3 e-14 Mean of measured intensity data Mars Perf Projection with nominal atmospheric and Moon Perf surface albedo Projection Measurement threshold Range (m)

GEN 3 NDL Performance Maximum LOS Rangea Maximum LOS Velocity Errorb LOS Range Errorb Data Rate Electronic Chassis Dimensions Optical Head Electronic Chassis. C Mass Optical Head Power (28 VDC) C > 4500 m 200 m/sec 0. 2 cm/sec 25 cm 20 Hz 28 x 22 x 20 cm 34 x 33 x 21 cm 8. 7 kg 5 kg 80 W a. Dependent on atmosphere and surface albedo b. Errors dominated by the vehicle’s vibration and angular motions (1. 7 cm/sec and 2. 2 m in flight tests) c. Heatsink and fans module for terrestrial operation adds 1. 5 kg and 10 W

Key NDL Features Ø Ø Ø Ø Stable, Narrow Linewidth, Low Noise Laser Stable and Low Noise Fiber Amp In-house built C&DH board 20 layers and thousands traces Highly Linear Modulation Waveform Low Noise, Flat Response, and Well-Balanced Receiver High Resolution FFT Processor Robust Signal Processing Algorithm Compact Chassis • Efficient Thermal Design • Mechanically Robust 3 -channel Dual-Balanced Receiver 11

Spaceflight Engineering Test Unit (ETU) Ø Ø Ø Use “space-qualified” or “space-qualifiable” parts Conduct radiation and thermal/vacuum tests at component/subsystem level Efficient heat conduction to host vehicle Robust structure EMI resistance NDL-3 ETU

Future Work Ø Complete and test Spaceflight Engineering Test Unit (ETU) by mid 2019 • Flight tests onboard a high speed aircraft and a rocket-powered vehicle in summer 2019 Ø Continue study and field testing for terrestrial applications • Autonomous ground aerial vehicles • Helicopter landing in degraded visual environments (DVEs) • Other proprietary applications Ø Continue technology advancement • Miniaturization • Expand NDL capabilities for other space and terrestrial applications 13

Backup 14

Principle of Navigation Doppler Lidar Frequency Modulated, Continuous Wave (FMCW) Technique Frequency Bandwidth Period Time delay is a measure of target range Detector Output (beat frequency) Target velocity causes up and down beat frequencies to separate Time

NDL Real-Time Processor & System Controller NDL Modulation Waveform

Comparison of NDL and MSL Radar Navigational Doppler Lidar Chassis MSL Doppler Radar Optical Head 24 cm m c 17 130 cm x 50 cm x 40 cm 35 cm 18 cm dia x 20 cm H MSL Radar NDL Mass (kg) 26 13 Power (W) 120 80 6 antennas each 22 cm diameter, 4 cm thick Optical Head Ø 30 X higher velocity and altitude precision Ø 3 orders of magnitude tighter beams Ø 40% reduction in power, 50% in mass, and 60% in size 17

Morpheus Flight Demonstrations § 3 -D Flash Lidar mapped the terrain for real-time hazard detection and avoidance Navigation Doppler Lidar Flash Lidar § NDL provided data for precision navigation and soft landing at the selected site § 3 open loop flights (April 2014) § 3 closed loop flights (two in May 2014 and one in December 2014) Doppler Lidar Head Approx. 450 m slant range 30 degree glideslope 100 m x 100 m hazard field Shuttle Landing Facility, NASA-KSC Laser Altimeter

Morpheus Flight Test Data Velocity Magnitude 350 300 Range (m) velocity (m/s) 16 12 8 Altitude 250 200 150 100 4 50 0 10 20 30 40 50 60 70 80 90 100 110 time (s) 0 10 20 30 40 50 60 70 80 90 100 110 time (s) Takeoff Landing

Comparison with IMU/GPS measurements NDL LOS velocity compared to vehicle NAV using IMU, GPS, and a laser altimeter 0. 2 LOS Residuals, m/sec 0. 15 0. 1 0. 05 0 -0. 05 -0. 15 -0. 2 0 10 20 30 40 50 60 70 80 80 100 110 Time, second Ø NDL data in excellent agreement with IMU/GPS/Altimeter data Ø NDL provides more accurate and precise vehicle state vector (position and velocity vector) than GPS Ø NDL surface-relative measurements are highly precise with negligible bias 20

Ongoing Free-Flyer Test Campaign COBALT Payload = NDL + Terrain Relative Navigation (TRN) sensor + Navigation Filter Altitude 500 m COBALT NDL 465 m Start 25 m/s descent Di v er 100 m t 10 m 20 m 300 m 21

Non-Space Applications of NDL Ø NDL can enable precision navigation in GPS-deprived environments Ø NDL can assist landing in degraded visual environments (DVEs) such as brownout condition Ø NDL can provide 3 -D range and velocity map of surroundings

Spaceflight Engineering Test Unit (ETU) Development Approach Ø Electronic parts • Use “space-grade” or “space-grade EM” parts • Few parts have no space-grade equivalents ‒ Change design or qualify COTS parts (i. e. , conduct radiation and thermal/vacuum tests) Ø Photonic and fiber optic parts • Leverage spaceflight qualification heritage when possible • Custom-design for space environments (vacuum, 0 g, radiation, thermal, vibration) • Conduct radiation and thermal/vacuum tests as necessary Ø Perform Th/Vac and Vibration tests on major subsystems Ø Subject assembled ETU Chassis to environmental tests 23